Cadillac STS Forum - 2005 through 2010Forum for discussions regarding the new Sigma-based STS model. Not for Cadillac "Seville" discussions (2004 and older).
Cadillac Forums: Different engine sound at hi revs and load
I just bought an 06 STS. A marvelous machine. Because (I think) of the variable valve timing, it has a long flat torque curve that starts early and ends late.
But there is a new-to-me sound to it at hi revs and load. The purr becomes the sound of a furiously fast machine gun! Is this normal? If so what causes it? It maintains strong torque in spite of the noise. The noise was not present in my 01 STS (fixed valve timing).
Is this normal? I use premium gas.
Same here, a real "snarl" when you stomp on the Loud pedal to accelerate onto an expressway, for instance. It's normal.
PS I use regular gas - the owner's manual says to do so and I haven't heard any convincing arguments against it. And what with the price of gas, it makes even more sense.
The only idea that I have for it is that it is optimum to have some intake and exhaust valve overlap at higher revs and load, so perhaps that is it. Either that or they have included a snarl machine in there to make it sound powerful!
My 2005 STS V8 has a very strange whooshing noise when you stomp it almost like wind going through a screen door, I asked the dealer about it and they said it was normal, yeah surprise, surprise. I've never heard an engine like that before, it's very noticeable with the top engine cover off, not as bad with it on, but it runs okay, I figured it was something with the OHC drive chains or something that's picking up high revolutions when you put the peddle to the metal.
generally speaking, vvt is used and has been used for many years as a compromise...a "have your cake and eat it too...somewhat"... vvt allows the engine to meet the emmissions standards and make more power at different ranges in the rpm band of the motor. vvt can be engineered to provide balls out performance and nothing else but since the engine must meed emmission standards, there's a compromise in the valve overlap which is the primary factor that the vvt impacts.
my 3.6 is tame and quiet until you stand on it and revs climb near the redline, then you can definitely hear the cams and the valves screaming....it doesn't hurt that the valve train is connected via chains rather than a belt; the noise level (good and bad, depending on your aural senses) is considerably reduced in a motor that has belts.
Thank you 'justgreat' for your thoughtful reply.
It doesn't sound like the mechanical jostling of valves being managed, or the scream of a chain engaging and disengaging gear teeth at sonic rates,to me. It sounds rather like I am hearing the combustion noise coming back through the intake manifold. I am wondering whether I am hearing the result of a weak or broken intake valve spring (leading to an intake valve that 'floats', somewhat, at higher revs), or whether this is the normal high rev overlap of intake and exhaust valves as the vvt optimizes valve timing to the rpm and load. This engine (2006 N*) is my first experience with vvt. Arguing against a valve spring problem is that it idles very smoothly, and never 'spits', and at normal highway speeds and accelerations the engine sounds quite civilized.
I put this question up on the forum because if it is normal, then a lot of other folks hear it too, and I can relax about it.
Thank you 'justgreat' for your thoughtful reply.
It doesn't sound like the mechanical jostling of valves being managed, or the scream of a chain engaging and disengaging gear teeth at sonic rates,to me. It sounds rather like I am hearing the combustion noise coming back through the intake manifold. I am wondering whether I am hearing the result of a weak or broken intake valve spring (leading to an intake valve that 'floats', somewhat, at higher revs), or whether this is the normal high rev overlap of intake and exhaust valves as the vvt optimizes valve timing to the rpm and load. This engine (2006 N*) is my first experience with vvt. Arguing against a valve spring problem is that it idles very smoothly, and never 'spits', and at normal highway speeds and accelerations the engine sounds quite civilized.
I put this question up on the forum because if it is normal, then a lot of other folks hear it too, and I can relax about it.
well, someone in this thread mentioned that they had the cover off the engine and that would definitely contribute to an increase in engine noise, that would get through to the passenger compartment.
when i bought my 76 alfa romeo alfetta gtv i was so concerned about the clatter noise coming from the engine compartment that i had the service manager take a look at it...he took a screw driver and put the shaft end on the cam cover and put his ear to the handle to listen to the motor...everything was fine. it was simply my lack of experience with a chain driven overhead cam, with the cam lobes directly on top of the valve buckets...much noisier than the setup used on current generation ohc engines.
i think your engine is fine..if you had any kind of valve train problems, believe me, you would know about it big time. the modern vvt engines are two for one: docile around town and screamers when you get on the cam...lots of great noises when you step into it.
